Many emerging micro-electro-mechanical systems (MEMS) require the construction of complex three-dimensional (3D) microstructures. The manufacture of these microstructures typically utilizes wafer bonding, including Si—Si fusion, Si—Si anodic, and Si-glass anodic bonding. However, the high bonding temperatures associated with Si—Si fusion bonding, which may exceed 1000° C., prevent the use of materials, such as metals and integrated electronics, that can not withstand these temperatures. On the other hand, although the temperatures of Si-glass bonding are typically below 400° C., it is typically more difficult to precisely machine the glass compared to silicon bonding. Furthermore, Si—Si, glass-glass, and Si-metal bonding at low temperature is still difficult to achieve. Si—Si anodic bonding has been achieved by depositing a thick glass layer on a silicon wafer. However, the deposition of glass in this manner is usually too time consuming and costly for commercial production.
In an attempt to overcome these problems, Si—Si anodic bonding with an evaporated thick glass layer as the bonding media has been previously used. However, this process requires glass deposition, high voltages, and high electric fields, which may potentially damage integrated circuits nearby. Therefore, there exists a need in the relevant art to construct complex MEMS structures with a bonding method that is simple and compatible with integrated circuit processes.
Furthermore, within somewhat related industries, micro jets are increasingly needed in such applications as micro propulsion, macro flow control, and cooling. In this regard, it is known to form micro jets using actuators fabricated through MEMS fabrication techniques. These actuators are capable of producing an instantaneous air velocity up to several meters per second. However, in order to produce a higher jet velocity at ultrasonic actuating frequencies, a forced Helmholtz resonator must be implemented. This device produces a maximum air velocity when operating at its resonant frequency. Earlier attempts to utilize such resonators by MEMS technology have attempted to fabricate them using a silicon-glass bonded structure. While other attempts having included fabricating a nozzle into a silicon wafer and bonding a flexible membrane to the silicon wafer that when resonated will create a jet of air. Although such devices were actuated at ultrasonic frequencies and despite achieving high acoustic field and an oscillation of flow at the resonator orifice were observed, any appreciable air velocity could not be obtained.
Therefore, there exists a need in the relevant art to provide a method of fabricating three-dimensional MEMS at low-temperatures that can be used in sensors, actuators, micro-machines, and other MEMS, including acoustic transducers. More particularly, there exists a need in the relevant art to provide a method of low-temperature, precision photolithography-patterned wafer bonding using photosensitive benzocyclobutene. Still further, there exists a need in the relevant art to overcome the disadvantages of the prior art.